In electric arc furnaces, such as those used in the manufacturing of steel, multiple phase alternating current electrical power is generally used to create thermal energy. In one example, three phase alternating current power is supplied to the furnace, with each electrode thereof receiving a respective one of the three phases. The alternating current electrical power of each respective phase is generally delivered from the power source to an electrode via a group, i.e. a plurality, of multiple conductor electrical cables, each of which may be a flexible water-cooled cable. In the event that one of the cables of a given group supplying the alternating current electrical power of a given phase were to deteriorate, for example with age or due to overheating, such that it carries less than its intended amount of current, one or more of the other cables in the group then may be required to carry excessive current that would damage the same. It is, accordingly, desirable to determine when a cable of such a group of cables, for example, has deteriorated to the point of near complete failure or has reached a point where it is causing overloading of the other cables in the group carrying the given phase of current, thereby causing increased deterioration of such other cables.
At present a principal reliable and practical procedure to check the condition of such cables includes the shut-down of the furnace, removal of each cable from the furnace, and the measuring of the resistance of each cable with a low range ohmmeter. This technique, however, is extremely time consuming and, additionally, requires the shut-down and subsequent restart of the furnace, thus reducing the operational efficiency of the latter.
According to another technique a separate current transformer is positioned about each of the cables of a group carrying a given phase of electrical power to the furnace. A separate voltmeter is attached to each such current transformer to indicate output information representative of the electrical current carried by the respective cables. This technique, however, also suffers from a number of disadvantages, including, for example, fluctuations in the output information with respect to frequently occurring fluctuations in the currents carried by the respective cables, the need for separate meters, the short, nearly instantaneous, life of the output information displayed by the meters, and so on. Often it is difficult or impossible to take such instantaneous readings using conventional metering equipment primarily because of the very large and frequently occurring fluctuations in current flow to an electric furnace.